By stating “bookcase” instead of “the Best bookshelves” or other descriptions, you imply a cabinet to store books.
There are several things to consider when designing a bookcase. The first is size. How tall and how wide will it be?
How To Design The Best BookShelves?
The width consideration: The reason width is a design consideration is that books are heavy. Items stored on each shelf will tend to deflect the shelf downward. In a small case, this isn’t too important, and the tray can be nothing more than a simple board.
In a full cabinet, each shelf-board will require some additional support. This can be as simple as adding a “skirt” under the shelf, i.e., a smaller board at a 90-degree angle that has the effect of giving the shelf added thickness without actually using a very thick board, which keeps the board from deflecting. It also helps keep the rack from warping over time.
The height consideration: The weight of many shelves in a high cabinet tends to make the sides bow outward. So, in a tall office, the parties need additional support. This can gain through several design approaches:
Have at least one fixed shelf in the middle of the bookcase to support the sides. Using a mechanical joint will be the most stable, i.e., use a dovetail or half-dovetail joint, and the case will not be able to bow outward.
Use a face-frame on the matter. This will strengthen the sides like having a skirt under shelf boards.
The choice of using a fixed shelf versus a face frame is that the face frame will have a more traditional look, and no face frame will have a more modern look.
The top and bottom of the case are subjected to similar stresses and should be attached using joinery that prevents the case sides from pushing outward. It can be as simple as adding a fixed shelf at or near the top and bottom of the case.
Some Important Things To Note
A bookcase can be subjected to racking forces, i.e., when being pushed sideways while fully loaded. Using fixed shelves in a case can support the entire case against racking through severe effects against a heavily loaded case that can still overstress the fact.
A face frame alone is not as durable, and adding a stable-solid back to the situation like plywood can add a lot of stability.
There are many designs for movable shelves from those you make yourself to those you can purchase through various outlets.
Online sources have numerous designs that you can view as well as training videos and articles. It is worthwhile exploring these to gain an insight into how you might want to proceed with the tools you have, can borrow, or can use at facilities that might be available for your use near where you live.